An electrostatic discharge protection device for protecting an inner circuit, which is operated in a source voltage, is provided and includes a protection unit and a control unit. The protection unit provides a discharge path for transmitting an electrostatic signal from a pad to a ground line. According to a voltage level at a control end, the protection unit adjusts a holding voltage and a triggering voltage determining whether to conduct the discharge path. When the source voltage is supplied, the control unit transmits the input voltage to the control end of the protection unit, so as to raise the holding and the triggering voltages of the discharge path. When the source voltage is not supplied, the control unit switches the control end of the protection unit to a floating condition by the electrostatic signal, so as to lower the holding and the triggering voltages of the discharge path.